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Late-onset autosomal recessive limb-girdle muscular dystrophy with rimmed vacuoles.

We report on two siblings with late-onset, limb-girdle muscular dystrophy (LGMD) inherited in an autosomal recessive manner. The LGMD was characterized by many rimmed vacuoles and reduced expression of the laminin beta1 chain in skeletal muscle. Both patients developed a progressive wasting and weakness of limb-girdle muscles in the late forties or early fifties; their facial, ocular, bulbar, and cardiac muscles were not involved. Histopathology of skeletal muscles biopsies showed typical dystrophic changes with many rimmed vacuoles. The immunoreactivity of the laminin beta1 chain was reduced in the muscle fibers, while dystrophin, sarcoglycans, beta-dystroglycan, dysferlin, and other laminin components were normally expressed. A mutation search revealed that no mutation existed in the coding region of the calpain 3, telethonin and UDP-N-acetylglucosamine 2-epimerase/N-acetylmanosamine kinase (GNE) genes. We conclude that this autosomal recessive LGMD is unknown and characterized by its late onset, rimmed vacuoles and reduction of the laminin beta1 chain in muscle fibers.

Actin Cytoskeleton↗

Clinical and genetic delineation of autosomal recessive and dominant ACTL6B-related developmental brain disorders.

PURPOSE: This study aims to comprehensively delineate the phenotypic spectrum of ACTL6B-related disorders, previously associated with both autosomal recessive and autosomal dominant neurodevelopmental disorders. Molecularly, the role of the nucleolar protein ACTL6B in contributing to the disease has remained unclear. METHODS: We identified 105 affected individuals, including 39 previously reported cases, and systematically analyzed detailed clinical and genetic data for all individuals. Additionally, we conducted knockdown experiments in neuronal cells to investigate the role of ACTL6B in ribosome biogenesis. RESULTS: Biallelic variants in ACTL6B are associated with severe-to-profound global developmental delay/intellectual disability, infantile intractable seizures, absent speech, autistic features, dystonia, and increased lethality. De novo monoallelic variants result in moderate-to-severe global developmental delay/intellectual disability, absent speech, and autistic features, whereas seizures and dystonia were less frequently observed. Dysmorphic facial features and brain abnormalities, including hypoplastic corpus callosum, and parenchymal volume loss/atrophy, are common findings in both groups. We reveal that in the nucleolus, ACTL6B plays a crucial role in ribosome biogenesis, particularly in pre-rRNA processing. CONCLUSION: This study provides a comprehensive characterization of the clinical spectrum of both autosomal recessive and dominant forms of ACTL6B-associated disorders. It offers a comparative analysis of their respective phenotypes provides a plausible molecular explanation and suggests their inclusion within the expanding category of "ribosomopathies."

Humans↗

Non-coding single-nucleotide and structural variants affecting the EYS putative promoter cause autosomal recessive retinitis pigmentosa.

PURPOSE: Variants in untranslated genomic regions are difficult to identify as pathogenic but are capable of causing disease by interfering with gene expression. This study aimed to characterize the effect of variants identified in the 5'-untranslated region of EYS in patients with autosomal recessive retinitis pigmentosa (RP). METHODS: Variant screening included gene panels, Sanger, exome, and genome sequencing. Functional validation included an electrophoretic mobility shift assay and various luciferase assays. RESULTS: Patients with RP from 6 EYS biallelic Arab-Muslim families harbored a 5' noncoding EYS variant, c.-453G>T, and 4 harbored a structural variant affecting the 5' noncoding exons. Electrophoretic mobility shift assay analysis revealed an effect on binding of transcription factors for c.-453G>T and a neighboring variant c.-454G>T. Dual luciferase assays using overexpression of various transcription factors showed distinct effects on expression. c.-453G>T was associated with higher luciferase expression with CRX overexpression and c.-454G>C with OTX2 overexpression. In addition, the 2 variants were found to influence translation by affecting upstream initiation codons. Interestingly, visual function of EYS RP patients who harbor c.-453G>T are better than those with biallelic null EYS variants. CONCLUSION: Our analysis revealed both single-nucleotide and structural variants in the EYS promoter as the cause of autosomal recessive RP. These variants may affect EYS expression via a dual mechanism by altering transcription factor binding affinity at the EYS promoter and by affecting upstream open reading frames.

Humans↗

Harlequin ichthyosis and other autosomal recessive congenital ichthyoses: the underlying genetic defects and pathomechanisms.

Autosomal recessive congenital ichthyoses (ARCI) include several severe subtypes including harlequin ichthyosis (HI), lamellar ichthyosis and non-bullous congenital ichthyosiform erythroderma. Patients with these severe types of ichthyoses frequently show severe hyperkeratosis and scales over a large part of the body surface form birth and their quality of life is often severely affected. Recently, research into the pathomechanisms of these severe congenital ichthyoses have advanced dramatically and led to the identification of several causative genes and molecules underlying the genetic defects. To date, seven loci have been identified that are associated with ARCI and, among them, five causative genes and molecules have been detected. The five genes are transglutaminase 1 gene (TGM1), ABCA12, two lipoxygenase genes, ALOXE3 and ALOX12B and ichthyin. One of these components, ABCA12, has recently been shown to be a keratinocyte lipid transporter associated with lipid transport in lamellar granules and loss of ABCA12 function leads to a defective lipid barrier in the stratum corneum, resulting in the HI phenotype. Transglutaminse 1 deficiency was reported to cause a malformed cornified cell envelope leading to a defect in the intercellular lipid layers in the stratum corneum and defective stratum corneum barrier function resulting in an ichthyosis phenotype. Thus, defective intercellular lipid layers are major findings in autosomal recessive congenital ichthyoses. Information concerning ARCI genetic defects and disease pathomechanisms are beneficial for providing better treatments and genetic counseling including prenatal diagnosis for families affect by ichthyoses.

ATP-Binding Cassette Transporters↗

Genetic basis of common diseases: the general theory of Mendelian recessive genetics.

Common diseases tend to appear sporadically, i.e., they appear in an individual who has no first or second degree relatives with the disease. Yet diseases are often associated with a slight but definite increase in risk to the children of an affected individual. This weak pattern of inheritability cannot be explained by conventional interpretations of Mendelian genetics, and it is therefore commonly held that there is "incomplete penetrance" of a gene, or that there are polygenic, or multifactorial modes of inheritance. However, such arguments are heuristic and lack predictive power. Here, we explore the possibility that "incomplete penetrance" means the existence of a second, disease-related, gene. By examining in detail a specific common condition, Parkinson's disease (PD), we show that the sporadic form of the disease can be fully explained by a compact fully penetrant genotype involving an interaction between two, and only two, genes. In this model, therefore PD is fundamentally genetic. Our digenic model is complementary to Mendelian recessive genetics, but taken together with the latter forms a complete description for recessive genetics on one chromosome. It explains the slight increase in risk to the children if one parent has sporadic PD, and makes strict predictions where both parents coincidentally have sporadic PD. These predictions were verified in two large and carefully selected kindred, where the data also argue against other genetic models, including oligogenic and polygenic schemes. Since the inheritance patterns of sporadic PD are reminiscent of what is seen in many common diseases, it is plausible that similar genetic forms could apply to other diseases. Seen in this light, diseases wash in and out of every family, so that in a sense, over time every human family is equally at risk for most diseases.

Family Health↗

Recessive, but not dominant, mutations in peripheral myelin protein 22 gene show unique patterns of aggregation and intracellular trafficking.

A characteristic feature of mouse models of the peripheral neuropathies caused by dominant mutations in peripheral myelin protein 22 (pmp22) is the appearance, in Schwann cells, of pmp22 aggregates. Using a set of dominant and recessive pmp22 mutations that cause human disease of varying degrees of severity, we compared their potential for aggregation and trafficking patterns with those of wild-type pmp22. The potential for aggregation was assessed by determining the size distribution of the various pmp22 mutant proteins under conditions where wild-type pmp22 showed little or no aggregation. All disease-causing dominant mutations showed significant aggregation and failed to traffic to the cell surface. Although the position of the dominant mutation in the pmp22 molecule determined both its potential for aggregation and how far it trafficked in the cell, there was no correlation between aggregation and the severity of the disease. On the other hand, recessive mutations were uniquely distinguished from dominant mutations by both the low potential for aggregation and their trafficking to the cell surface. In the course of these studies, it was also noted that the potential for aggregation and the trafficking of mutant pmp22s is influenced by the nature and/or location of the epitope tag.

Animals↗

Early transposable element insertion in intron 9 of the Hsf4 gene results in autosomal recessive cataracts in lop11 and ldis1 mice.

Lens opacity 11 (lop11) is an autosomal recessive mouse cataract mutation that arose spontaneously in the RIIIS/J strain. At 3 weeks of age mice exhibit total cataracts with vacuoles. The lop11 locus was mapped to mouse chromosome 8. Analysis of the mouse genome for the lop11 critical region identified Hsf4 as a candidate gene. Molecular evaluation of Hsf4 revealed an early transposable element (ETn) in intron 9 inserted 61 bp upstream of the intron/exon junction. The same mutation was also identified in a previously mapped cataract mutant, ldis1. The ETn insertion altered splicing and expression of the Hsf4 gene, resulting in the truncated Hsf4 protein. In humans, mutations in HSF4 have been associated with both autosomal dominant and recessive cataracts. The lop11 mouse is an excellent resource for evaluating the role of Hsf4 in transparency of the lens.

Animals↗

Defective splicing of Megf7/Lrp4, a regulator of distal limb development, in autosomal recessive mulefoot disease.

Mulefoot disease (MFD) is an autosomal recessive disorder of phenotypically variable expression that causes syndactyly in certain strains of cows. MFD maps to a narrow interval on bovine chromosome 15 that is syntenic to human chromosome 11p12-p11.2. This region contains MEGF7/LRP4 (approved gene symbol LRP4), a gene that encodes a member of the multifunctional low-density lipoprotein receptor gene family. Targeted and naturally occurring mutations in the murine Megf7/Lrp4 gene, a putative coreceptor in the Wnt signaling pathway, cause polysyndactyly in the rodent. Thus, Megf7/Lrp4 is a strong candidate for the MFD mutation. Using PCR analysis of tissue samples and sperm from confirmed homozygous MFD carriers, we have identified a functional single base pair mutation in the affected animals. We show that a G --> A transition at the first nucleotide in the splice donor site of intron 37 completely disables this splice site. The abnormal splicing that is caused by this mutation predicts the generation of a dysfunctional membrane-anchored receptor lacking the normal cytoplasmic domain. These findings confirm that autosomal recessive loss-of-function mutations in Megf7/Lrp4 result in phenotypically similar forms of syndactyly in different mammalian species and that such mutations are the cause of MFD in bovines.

Amino Acid Sequence↗

Sepiapterin reductase deficiency an autosomal recessive DOPA-responsive dystonia.

The diagnosis of a 14-year-old girl with a new homoallelic mutation in the sepiapterin reductase (SR) gene is reported. Initially she presented at the age of 2 with hypotonia and mild cognitive developmental delay, and was diagnosed as having mild methylmalonic aciduria, which was recently identified as methylmalonylCoA racemase deficiency, a new defect in valine-isoleucine metabolism. After a 12-year progression of her neurologic condition, which had made her wheelchair-bound at the age of 6, dystonia with diurnal variation had become apparent. At the age of 14 this finding led to rapid diagnosis of SR deficiency. The diagnostic approach with CSF neurotransmitter and pterins analysis and combined phenylalanine/BH(4) loading test, and finally measurement of sepiapterin in CSF is illustrative for the diagnosis of SR deficiency. As in all other patients with this new defect, very low levels of homovanillic acid and 5-hydroxyindoleacetic acid and high levels of biopterin and sepiapterin in the CSF are the diagnostic hallmark. The girl improved dramatically on treatment with L-DOPA and 5-hydroxytryptophan. The initial diagnosis of methylmalonic aciduria may afterwards be considered to have not significantly contributed to her clinical condition and only has led to a long delay of the clinically relevant diagnosis of SR deficiency. Although the clinical condition of this recently recognized autosomal recessive defect in pterin metabolism is complex and many symptoms can occur in variable severity and time of onset, dystonia with diurnal variation is a characteristic finding, as shown in nearly all patients described so far. The rapid and favourable response on treatment with L-DOPA warrants the classification of SR deficiency as another autosomal recessive type of DOPA-responsive dystonia (DRD). This classification is important to improve the awareness of clinicians that more than one metabolic defect can underlie the phenotype of a DOPA-responsive dystonic disorder and that dystonia should always trigger a rapid diagnosis of the underlying neurotransmitter synthesis defect, in view of the excellent treatability of a DRD.

Adolescent↗

Autosomal recessive cerebellar ataxia with oculomotor apraxia (ataxia-telangiectasia-like syndrome) is linked to chromosome 9q34.

Ataxia with oculomotor apraxia (ataxia-telangiectasia-like syndrome [AOA]; MIM 208920) is an autosomal recessive disorder characterized by ataxia, oculomotor apraxia, and choreoathetosis. These neurological features resemble those of ataxia-telangiectasia (AT), but in AOA there are none of the extraneurological features of AT, such as immunodeficiency, neoplasia, chromosomal instability, or sensitivity to ionizing radiation. It is unclear whether these patients have a true disorder of chromosomal instability or a primary neurodegenerative syndrome, and it has not been possible to identify the defective gene in AOA, since the families have been too small for linkage analysis. We have identified a new family with AOA, and we show that the patients have no evidence of chromosomal instability or sensitivity to ionizing radiation, suggesting that AOA in this family is a true primary cerebellar ataxia. We have localized the disease gene, by linkage analysis and homozygosity mapping, to a 15.9-cM interval on chromosome 9q34. This work will ultimately allow the disease gene to be identified and its relevance to other types of autosomal recessive cerebellar ataxias to be determined.

Acid Anhydride Hydrolases↗

Autosomal recessive cerebellar ataxia with bull's-eye macular dystrophy.

PURPOSE: In 1980, we published in the American Journal of Ophthalmology two siblings with hereditary ataxia and atrophic maculopathy. The report is cited in the literature as autosomal dominant cerebellar ataxia with retinal degeneration. The purpose of the present study is to document the progression of the neurodegenerative disorder and to review the diagnosis. DESIGN: Observational case report. METHODS: Twenty years after the original publication, the 52-year-old male patient had new ocular and neurologic examinations, fluorescein angiography, molecular genetic analysis, and biochemical testing. RESULTS: Fluorescein angiography showed marked progression of the macular dystrophy to a bull's-eye configuration. Genetic analysis of the patient did not show CAG trinucleotide repeat expansion in the various spinocerebellar ataxia genes. This excludes the diagnosis of autosomal dominant cerebellar ataxia with macular degeneration (ADCA type II) with mutation of the spinocerebellar ataxia 7 gene. Major causes of autosomal recessive cerebellar ataxia with retinal degeneration, including Friedreich ataxia and congenital disorders of glycosylation, were also excluded. CONCLUSION: The two patients, previously published in the American Journal of Ophthalmology by Eerola and coworkers, did not suffer from presently recognized disorders with cerebellar ataxia and retinal degeneration. The Eerola syndrome probably represents a separate neurodegenerative entity characterized by autosomal recessive cerebellar ataxia and progressive macular dystrophy with a bull's-eye pattern.

Cerebellar Ataxia↗

A missense mutation in canine C1C-1 causes recessive myotonia congenita in the dog.

Myotonia congenita is an inherited disorder of sarcolemmal excitation leading to delayed relaxation of skeletal muscle following contractions. Mutations in a skeletal muscle voltage-dependent chloride channel, CIC-1, have been identified as the molecular genetic basis for the syndrome in humans, and in two well characterized animal models of the disease: the myotonic goat, and the arrested development of righting (adr) mouse. We now report the molecular genetic and electrophysiological characterization of a canine CIC-1 mutation that causes autosomal recessive myotonia congenita in miniature Schnauzers. The mutation results in replacement of a threonine residue in the D5 transmembrane segment with methionine. Functional characterization of the mutation introduced into a recombinant CIC-1 and heterologously expressed in a cultured mammalian cell line demonstrates a profound effect on the voltage-dependence of activation such that mutant channels have a greatly reduced open probability at voltages near the resting membrane potential of skeletal muscle. The degree of this dysfunction is greatly diminished when heterodimeric channels containing a wild-type and mutant subunit are expressed together as a covalent concatemer strongly supporting the observed recessive inheritance in affected dog pedigrees. Genetic and electrophysiological characterization of the myotonic dog provides a new and potentially valuable animal model of an inherited skeletal muscle disease that has advantages over existing models of myotonia congenita.

Amino Acid Sequence↗

Multicenter genetic study of retinitis pigmentosa in Japan: II. Prevalence of autosomal recessive retinitis pigmentosa.

Retinitis pigmentosa (RP) is a group of genetically heterogeneous diseases with autosomal recessive (AR), autosomal dominant, and X-linked modes of inheritance. Autosomal recessive retinitis pigmentosa (ARRP) is the most common form in Japan. A genetic analysis was done to determine the prevalence of ARRP indirectly, to provide an estimation of changing trends in the overall prevalence of RP. Data on the frequency of consanguinity and marriage year of normal parents of 59 ARRP patients were obtained from a nationwide multicenter survey of typical retinitis pigmentosa conducted in 1990. The gene frequency of ARRP was 0.01145 (Dahlberg's formula). In 1990, the number of young symptomatic ARRP patients decreased, while the number of patients aged 40 years and older increased. The total number of symptomatic ARRP patients in 1990 was nearly 21% higher than in 1970. Despite a dramatic decline in consanguinity in recent decades in Japan, the number of ARRP patients has increased. This increase is attributed to greater longevity and overall population growth. Our results suggest that the total number of RP patients has not decreased, and may even have increased.

Adolescent↗

Familial diaphragmatic agenesis: an autosomal-recessive syndrome with a poor prognosis.

Diaphragmatic agenesis is a severe form of congenital diaphragmatic hernia for which an autosomal recessive form of inheritance has been proposed. The authors report six families with 13 pregnancies with diaphragmatic agenesis in which inheritance followed an autosomal recessive pattern, including the first reported case of bilateral diaphragmatic agenesis in twins. None of the thirteen affected fetuses survived. Familial diaphragmatic agenesis appears to be a distinct clinical entity with a worse prognosis than posterolateral diaphragmatic hernia.

Adult↗

Familial and sporadic hyperinsulinism: histopathologic findings and segregation analysis support a single autosomal recessive disorder.

We evaluated the possible genetic contribution to hyperinsulinism in a series of patients seen during the past 15 years. Of 26 families, 5 (19%) had more than one child affected (multiplex family). There were no apparent differences between patients in the 5 multiplex and 21 simplex families, clinically, biochemically, or on histologic examination of the pancreatic specimens. The families studied had a total of 63 offspring; the 26 index patients had 37 siblings, 6 of whom were affected. After four patients with hyperinsulinism caused by adenoma were excluded from the study, segregation analysis was carried out to test the data for agreement with results expected if familial and isolated hyperinsulinism represented a single disease with recessive mode of inheritance and a segregation ratio of 0.25. Excellent agreement was found between the observed number of affected siblings (20) and the expected number (19.65), with a segregation ratio of 0.254. The results were consistent with the hypothesis that in most or all cases, hyperinsulinism is inherited as an autosomal recessive disease. There was no evidence of distinct familial and sporadic types.

Family Characteristics↗

Gingival recession related to removable partial dentures in older patients.

One hundred forty-six patients, living in the community and attending a general dental practice, were examined on two occasions separated by 3 years to determine relationships among removable partial dentures, their design, and gingival recession. This study confirmed the relationship between the presence of a partial denture and an increase of gingival recession, but was unable to demonstrate any predictable relationship to the lack of tooth support, the material used for the dentures, or covering the gingival margins with lingual plates. These design factors may be less important than the maintenance of good oral hygiene for the prevention of periodontal disease in patients wearing removable partial dentures.

Age Factors↗

Alternative method of conservative esthetic treatment for gingival recession.

The health and appearance of gingival tissue play an essential role in esthetics. The esthetic function of the tissue is enhanced when it frames the restoration. With gingival recession, the effect of natural gingiva is created with pink composites or ceramics on the cervical part of the crown, as described in this clinical report. This goal depends on the absence of adverse effects on the color, shape, and health of the surrounding tissue. The new composites are more color stable and wear resistant, and the latest generation of dental bonding agents allows the bonding of composites to dentin, various metals, and porcelain. The application of soft-tissue colored composite on dentin cementum, enamel, or porcelain is a good solution for correcting gingival recessions.

Acid Etching, Dental↗

[Molecular analysis of the RPE65 gene in 72 Spanish families with autosomal recessive retinitis pigmentosa].

BACKGROUND: Autosomal recessive retinitis pigmentosa (arRP) is the most common form of retinitis pigmentosa (RP). It is characterized by a high degree of allelic and non-allelic genetic heterogeneity. Previously,it has been demonstrated that the RPE65 gene is responsible for 2% recessive or isolated RP cases and 16% Leber's congenite amaurosis cases. Although the concrete function of RPE65 is unknown as yet, it has been found to be involved in vitamin A metabolism and rhodopsin regeneration. PATIENTS AND METHOD: We studied the involvement of the RPE65 gene in 72 arRP Spanish families by means of indirect molecular and mutation analysis. RESULTS: The results obtained using the intragenic microsatellite marker D1S2803 allowed us to exclude RPE65 as the causative gene of the disease in 80.5% of the families studied. Three new variants of the RPE65 gene have been identified: IVS6-43delA, IVS6-42delT and IVS6-33CG. We found that IVS6-33C-->G was a common polymorphism. The other variants, namely IVS6-43delA and IVS6-42delT, were not identified in 150 control chromosomes studied. The segregation analysis of IVS6-42delT variant seemed to exclude it as being involved in the disease. CONCLUSIONS: Our results argue against the involvement of RPE65 gene in the families studied, indicating that the prevalence of RPE65 abnormalities in arRP Spanish families may be lower than that observed in other populations.

Carrier Proteins↗